1. Field of the Invention
The present invention relates, in general, to optical pick-up actuators for focusing and tracking the object lens of an optical pick-up device relative to a disc while reading or writing information from or onto the disc and, more particularly, to an optical pick-up actuator having a blade, which is installed to float above a yoke plate and be tiltable relative to the yoke plate, thus allowing the pick-up device to precisely read or write information from or onto a high density disc even when the disc is inclinedly positioned in the deck of a disc player.
2. Description of the Prior Art
As well known to those skilled in the art, an optical pick-up actuator is an actuating element of an optical pick-up device, which moves the object lens of the pick-up device in a radial direction to find a desired track of a disc and moves the lens in an axial direction to adjust the size of a focused beam spot on the disc as desired, thus adjusting the optical spot of a laser beam in case of occurrence of an axial positioning error and/or a radial positioning error of the laser beam spot formed on a recording pit of the disc by the laser beam radiated from a laser diode of the pick-up device through the object lens.
Of conventional optical pick-up actuators having a lens drive mechanism, an optical pick-up actuator used in DVD players has been required to have a high drive precision in accordance with the recent trend of an increase in the density of recording pits formed on the tracks of a disc.
That is, the blade of such an optical pick-up actuator, designed to appropriately focus a laser beam on a disc using its object lens under the drive of the actuator""s drive mechanism, is provided with a magnet for forming a magnetic flux. Due to the magnetic flux from the magnet, the blade having the object lens is electromagnetically moved in a vertical direction relative to a yoke plate by means of a focusing coil, moved in a radial direction by means of a tracking coil, and tilted in accordance with an angle of inclination of a disc installed within a disc player.
FIG. 1 shows the construction of a conventional wire-driven optical pick-up actuator. As shown in the drawing, a lens holder 140 or a so-called xe2x80x9cbladexe2x80x9d, fixedly holding an object lens 142, is supported on a yoke plate 110 by a plurality of suspension wires 130 such that the blade 140 is movable on the yoke plate 110. The object lens 142 is set in the center of the blade 140, while a focusing coil 144 is horizontally wound around the blade 140. Two tracking coils 146, each having a rectangularly coiled structure, are attached to opposite sides of the focusing coil 144.
Two coil PCBs 148 are mounted to opposite sides of the blade 140 while being angularly spaced apart from the two tracking coils 146 at right angles, thus connecting the tracking coils 146 to the focusing coil 144. Two symmetrical external yokes 114 are formed on the yoke plate 110, while a magnet 118 is mounted to each external yoke 114 through a bonding process. The two magnets 118 apply magnetic fluxes to both the focusing coil 144 and the two tracking coils 146, thus generating electromagnetic force in the actuator. Two symmetrical internal yokes 112 are formed on the yoke plate 110 such that the two internal yokes 112 extend upward from the yoke plate 110 at positions spaced apart from the external yokes 114 by a predetermined gap, thus guiding the flow of magnetic fluxes from the magnets 118 in the actuator. Therefore, the above optical pick-up actuator forms a closed magnetic circuit, in which the magnetic fluxes from the magnets 118 strongly pass through the coils 146 and 144 in a horizontal direction, and pass along the planar surfaces of both the internal yokes 112 and the yoke plate 110 prior to being returned to the magnets 118.
A second yoke 116 is provided at a side edge of the yoke plate 110 for supporting both a wire holder 120 and a suspension PCB 122 using a plurality of setscrews. The first end of each suspension wire 130 is connected to an associated coil PCB 148 of the blade 140, while the second end of each wire 130 is connected to the wire holder 120. The blade 140 thus floats on the yoke plate 110 by means of the suspension wires 130. In an operation of the optical pick-up actuator, a current applied from a signal processing unit to the suspension PCB 122 is also applied to both the tracking coils 146 and the focusing coil 144 through the suspension wires 130.
In order to horizontally move the blade 140 of such an optical pick-up actuator on the deck of a CD player or a DVD player, the yoke plate 110 is locked to a pick-up base (not shown), which is installed on the deck so as to be movable on the deck. The optical pick-up actuator moves the object lens relative to a disc as required during a data reading or recording operation of the pick-up device.
However, the wire-driven optical pick-up actuator, operated by both the tracking coils and the focusing coil, is problematic as follows, particularly when the actuator is used with a DVD player for playing an optical disc having densely packed recording pits. That is, the movable range of the blade of such an actuator is determined by both the tracking coils and the focusing coil, and so it is very difficult for a pickup device with such an actuator to write information on an optical disc.
In other words, it is almost impossible for the conventional wire-driven pick-up actuator to tilt the object lens when it is desired to precisely align the optical path of the lens with a disc in the case of the disc inclinedly seated in a disc player. In an effort to overcome such a problem of the conventional wire-driven actuators, another drive mechanism for optical pick-up actuators used in CD players has been proposed. This drive mechanism has an improved blade structure and six or more suspension wires, and controls the blade tilting, direction in response to a current direction flowing through the suspension wires. However, this actuator structure is problematic in that it has a complex construction, thus complicating the operational precision test process for the actuators and deteriorating the operational reliability of the pick-up actuators.
The blade tilting operation of the optical pick-up actuator is performed to align the optical path of an object lens with a disc when the disc is driven in a disc player while being inclined. Particularly, it is necessary for an optical pick-up actuator to perform such a blade tilting operation when it is used with a disc having a high recording density or densely packed recording pits.
In recent years, a magnet-driven pick-up actuator, designed to perform such a blade tilting operation in addition to performing a vertical and radial movement of the blade relative to a yoke plate, has been proposed and preferably used in accordance with the use of high capacity optical discs or high density recording discs. In a conventional magnet-driven pick-up actuator, a blade, installed above a yoke plate and having a focusing coil, two tracking coils and an object lens, is also provided with a drive magnet for controlling the vertical movement, radial movement and tilting action of the blade relative to the yoke plate in accordance with a current-induced magnetic field of each of the focusing and tracking coils. However, such a conventional magnet-driven pick-up actuator is problematic in that it is reduced in its operational performance since its magnetic circuit does not form any closed loop, but has a large void.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an optical pickup actuator, which is used for focusing and tracking its object lens relative to a disc while reading or writing information from or onto the disc, and the blade of which is installed to float above a yoke plate and be effectively tiltable relative to the yoke plate, thus allowing the object lens to be aligned with a high density disc and allowing an optical pick-up device to precisely read or write information from or onto the disc even when the disc is inclinedly positioned in the deck of a disc player.
In order to accomplish the above objects, the present invention provides an optical pick-up actuator, comprising: a blade having an object lens at its top center for focusing light, the blade also having a drive coil unit around its outside surface and a plurality of magnet seating holes on opposite sides of its lower surface; a tilting magnet held in each of the magnet seating holes of the blade; a plurality of suspension wires allowing a current to flow therethrough and supporting the blade; a wire holder supporting one end of each of the suspension wires; a side yoke provided at a position vertically aligned with each of the tilting magnets held in the magnet seating holes of the blade; a tilting coil held on the side yoke and electromagnetically tilting the blade at a desired angle relative to the perpendicular optical path of the object lens; a drive magnet forming a magnetic field in the drive coil unit of the blade; internal and external yokes holding the drive magnet and determining the range of the magnetic field formed in the drive coil unit, the internal and external yokes being integrated into a single structure; and a yoke plate having a beam passing hole at its central area aligned with the optical path of the object lens, thus allowing a light beam from the object lens to pass through, the yoke plate also holding the wire holder thereon.